Dynamic effective radiated power (erp) adjustment

ABSTRACT

Antennas used aboard aircraft to communicate with satellites or ground stations may have complex antenna patterns, which may vary as the aircraft moves throughout a given coverage area. Techniques are disclosed for dynamically adjusting the instantaneous power fed to an antenna system to ensure that the antenna transmits at the regulatory or coordinated effective isotropic radiated power (EIRP) spectral limit. The antenna may transmit, in accordance with aircraft location and attitude, steerable beam patterns at different scan and skew angle combinations, causing variations in antenna gain and fluctuations in the transmitted EIRP. Using on-board navigational data, an antenna gain and ESD limit may be calculated for a particular scan and skew angle, which may be used to adjust power fed to the antenna such that the antenna transmits substantially at maximum allowable EIRP as the steerable beam pattern is adjusted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application No.62/357,570, entitled “Dynamic Effective Radiated Power (ERP)Adjustment,” and filed on Jul. 1, 2016, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure describes a means to continuously adjust thedynamic range of a station based on location, attitude (roll, pitch,yaw), and antenna characteristics, such that the instantaneous maximumoutput power available to the station corresponds to the regulatory orcoordinated effective isotropic radiated power (EIRP) spectral densitylimit.

BACKGROUND

For certain types of stations such as earth stations aboard aircraft(ESAA), for example, transmission towards a satellite (or ground-basedstations) is limited by off-axis effective isotropic radiated power(EIRP) spectral density (ESD). That is, to prevent interference withadjacent satellites or ground-based stations, earth stations aboardaircraft (ESAAs) must comply with limitations on off-axis ESD. Theselimitations, which are typically stated as a mask specifying a maximumallowable ESD at a given angular offset along the geostationary orbit(GSO) arc, may either be coordinated with the operators of the adjacentsatellites or mandated by a regulatory authority. Some phased-arrayantennas, such as those used in ESAA systems, exhibit isogain contourellipticity and gain variation as a function of elevation. Due to theunique requirements associated with the airborne environment, theantennas used on board aircraft for communications may have complexantenna patterns that may vary as the aircraft moves throughout a givencoverage area. As a consequence, the variations of antenna gain resultin ESD limits that vary as a function of scan angle, skew angle, andfrequency.

Adaptive, time-division duplexed multiple access (aTDMA) air interfacesmay vary the coding, modulation, and symbol rate of transmissions froman ESAA to accommodate changes in the prevailing channel conditions, andother substantial capacity benefits on the link from the aircraft to theserving satellite (the “inroute”). However, since aTDMA transmissionscan vary in frequency, power, and bandwidth on very short timescales,they introduce significant complexities in the monitoring of the ESAA'sinstantaneous ESD.

Furthermore, another method to meet the ESD limit is to select a minimumESD limit over all operating conditions (i.e., scan angles, skew angles,and frequencies) used to transmit toward a particular target, and tocalculate an antenna power input level using this minimum ESD limit.Providing power to the antenna using this minimum ESD thus ensures thatthe ESAA will meet the ESD limit for all scan/skew angle combinations asthe antenna gain varies. However, this method has proven to beinflexible because it limits transmission to below the ESD limit forother scan/skew combinations when, for example, an ESAA antennaexhibiting a variable gain is capable of transmitting at the ESD limitacross other scan/skew angles but is otherwise limited by the poweroutput calculated in accordance with the minimum ESD.

BRIEF SUMMARY

Stations, such as ESAAs, for example, may be utilized to supplementvehicle communications. For aircraft, ESAAs may be integrated with otheraircraft components and provide wireless communication links between theaircraft and ground-based networks via communication with satellitesand/or ground stations. Through communication with the ground-basednetworks, ESAAs may provide aircraft with various wireless connectivityservices for the airline passengers and/or crew, such as Internetaccess, text messaging, Wi-Fi, etc.

To do so, the ESAA maintains one or more wireless links with varioustargets such as satellites and/or ground-based stations during flight.Similar to mobile device handoffs, the ESAA may switch communicationswith satellites and/or ground-based stations based upon networkcapacity, signal strength, and/or line-of-sight considerations, forexample. To accomplish communications with different targets in thismanner, ESAAs typically have one or more antennas that are configured totransmit and/or receive signals in accordance with a steerable beampattern. This beam pattern may be controlled by one or more processorsto electronically and/or mechanically steer the antenna towards adesired target.

However, as the antenna is steered towards a particular target while theaircraft moves throughout a given coverage area, the antenna gain mayvary. For example, at a particular scan angle, φ, the gain of an antennaused in an ESAA may vary with changes in the skew angle ψ, as a resultof changing aircraft attitude. And this gain may further vary across arange of skew angles at a different scan angle. In other words, althoughthe ESAA antenna may be steered towards various targets during flight,doing so results in variations in the antenna gain for different scanand skew angle combinations. The off-axis effective isotropic radiatedpower (EIRP) for an ESAA at a particular scan and skew angle is afunction of antenna gain and the instantaneous antenna power input.Therefore, as the gain of the antenna varies with changes in scan andskew angle combinations, so does the EIRP.

Therefore, to compensate for these antenna gain variations whilemaintaining the regulatory or coordinated ESD, techniques are disclosedto dynamically adjust the instantaneous power fed to an antenna systemthat forms part of a station (e.g., an earth station aboard aircraft(ESAA)). Again, the EIRP is limited by a maximum ESD limit, which may beset by a regulatory agency such as the Federal Communications Commission(FCC), for example. Furthermore, a minimum ESD may be driven by systemperformance such that, at a selected minimum ESD, the corresponding EIRPyields an acceptable threshold throughput, for example. Thus, for agiven system, the transmitted EIRP may vary between a minimum EIRP (inaccordance with the minimum ESD) and a maximum EIRP (in accordance withthe maximum ESD limit). To ensure that the antenna transmits at anoptimum effective isotropic radiated power (EIRP), the antenna inputpower may be varied with changes in the antenna gain and the ESD limitfor various new scan and skew angle combinations as a result of ESAAlocation, aircraft attitude, and antenna characteristics.

To accomplish this, navigational data from the aircraft may be leveragedto calculate a target scan and skew angle in the direction of a targetsatellite or ground-based station. Once these new target scan and skewangles are known, embodiments include calculating the corresponding ESDlimit and instantaneous maximum output power available to the stationfor this new target scan and skew angle, as these metrics change as afunction of scan and skew angle in accordance with the location,aircraft attitude, and characteristics of a particular antenna. Andbecause the antenna input power required to maintain a particular EIRPis a function of both the ESD limit and the antenna gain at a particularscan and skew angle, the instantaneous antenna input power may becalculated once the ESD limit and antenna gain for this new target scanand skew angle are known. Therefore, as the steerable beam pattern isadjusted while the attitude of the aircraft changes as it movesthroughout a given coverage area, embodiments include optimizing thetransmitted EIRP by adjusting the instantaneous antenna power input toensure that the transmitted EIRP is substantially equal to the maximumallowable EIRP over a range of scan and skew angles.

The amplifier instantaneous power output may be used to provide antennainput power, which may be measured to calculate the transmitted EIRP andused to verify that the transmitted EIRP is less than a maximumallowable transmitted EIRP based upon the ESD limit for the target scanangle and the target skew angle. In the event that the transmitted EIRPexceeds the maximum allowable transmitted EIRP, the amplifierinstantaneous power output may be reduced accordingly.

Throughout the disclosure, the term “EIRP,” or effective isotropicradiated power, is used as regulatory agencies typically use thisterminology. However, it will be understood that the embodimentsdiscussed herein may be modified to be applicable to any measurement ofeffective radiated power (ERP) in an antenna system. For example, thetechniques described herein are equally applicable to systems thatutilize an ideal dipole reference for an ERP calculation as opposed toan ideal isotropic radiator.

Furthermore, advantages will become more apparent to those of ordinaryskill in the art from the following description of the preferredembodiments which have been shown and described by way of illustration.As will be realized, the present embodiments may be capable of other anddifferent aspects, and their details are capable of modification invarious respects. Accordingly, the drawings and description are to beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example communication system 100 in accordancewith an embodiment of the present disclosure;

FIG. 2 illustrates a block diagram of a station 200 in accordance withan embodiment of the present disclosure;

FIG. 3 illustrates a method flow 300 illustrating the amplifierinstantaneous output power calculations for new target scan and skewangles in accordance with an embodiment of the present disclosure;

FIG. 4A illustrates an example plot 400 showing changes in the effectiveisotropic radiated power (EIRP) limit, EIRP maximum, and EIRP minimumover a range of skew angles for a constant scan angle, in accordancewith an embodiment of the present disclosure; and

FIG. 4B illustrates an example plot 450 showing changes in the amplifierinstantaneous output power over a range of skew angles for a constantscan angle, in accordance with an embodiment of the present disclosure.

The figures depict aspects of the present invention for purposes ofillustration only. Alternate aspects of the structures and methodsillustrated herein may be employed without departing from the principlesof the invention described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates an example communication system 100 in accordancewith an embodiment of the present disclosure. In the presentembodiments, communication system 100 may include a vehicle 102, anysuitable number N of satellite communication systems 104.1-104.N, anysuitable number M of ground-based stations 112.1-112.M, and aground-based network 110. Communication system 100 may includeadditional, less, or alternate components, including those discussedelsewhere herein. Furthermore, for the sake of brevity, communicationsystem 100 is illustrated as including a single vehicle 102. However,the aspects described herein may include any suitable number of suchvehicles.

Vehicle 102 may include one or more stations 103 and/or 105, as shown inFIG. 1. Stations 103 and/or 105 may be mounted to, located within, orotherwise associated with vehicle 102 to facilitate communicationsbetween vehicle 102, one or more satellite communication systems104.1-104.N, and/or one or more ground-based stations 112.1-112.M. In anembodiment, stations 103 and/or 105 may be implemented as respectiveESAAs associated with the aircraft in which they are implemented, suchas vehicle 102, for example. Although two stations 103 and 105 are shownin FIG. 1, embodiments include vehicle 102 implementing any suitablenumber of stations (e.g., one station or more than two).

Furthermore, the illustration provided in FIG. 1 is for illustrativepurposes, as embodiments include stations 103 and/or 105 being mountedto any suitable portion of vehicle 102 such as, for example, beneath thevehicle, above the vehicle, etc. Furthermore, although vehicle 102 isshown in FIG. 1 as an aircraft, embodiments include stations 103 and/or105 being implemented in any suitable type of vehicle in which asteerable antenna system may be implemented to facilitatecommunications, which may include airborne, land, and/or water-bornevehicles such as a space vehicle, a truck, a train, an automobile, abus, a ship, a military vehicle, etc.

Vehicle 102 may utilize stations 103 and/or 105 to communicate withground-based network 110 in any suitable manner to obtain variousservices provided by ground-based network 110 and to provide theseservices to passengers and/or crew of vehicle 102. For example,ground-based network 110 may provide vehicle 102 with connectivity toInternet services during flight such as email, streaming media, instantmessaging, etc. These services may be provided to various computingdevices located within vehicle 102, for example, via any suitable wiredand/or wireless communication protocol, such as an IEEE 802.11 standardcompliant protocol (e.g., Wi-Fi), for example.

In an embodiment, stations 103 and/or 105 may be configured to transmitand/or receive data in accordance with any suitable number and/or typeof communication protocols to facilitate communications with one or moresatellite communication systems 104.1-104.N and/or one or moreground-based stations 112.1-112.M. For example, as will be discussedfurther below with reference to FIG. 2, stations 103 and/or 105 may beimplemented with any suitable combination of hardware and/or software tofacilitate these functions such as, for example, one or more modems,upconverters, downconverters, amplifiers, processors, antennas, etc. Inan embodiment, stations 103 and/or 105 may be configured to transmitand/or receive data in accordance with any suitable frequency or band offrequencies. For example, stations 103 and/or 105 may be configured totransmit and/or receive data in accordance with the Ku microwave band.

In various embodiments, ground-based network 110 may be configured tofacilitate communications between stations 103 and/or 105 and/or one ormore satellite communication systems 104.1-104.N using any suitablenumber of wireless links, as shown in FIG. 1. For example, ground-basednetwork 110 may include any suitable number of nodes, additional wiredand/or wireless networks that may facilitate one or more landlineconnections, internet service provider (ISP) backbone connections,satellite links, public switched telephone network (PSTN), etc. Toprovide additional examples, ground-based network 110 may be implementedas one or more local area networks (LANs), one or metropolitan areanetworks (MANs), one or wide area networks (WANs), or any suitablecombination of local and/or external network connections.

To facilitate communications between stations 103 and/or 105 and/or oneor more satellite communication systems 104.1-104.N, ground-basednetwork 110 may be coupled to or otherwise communicate with one or moreground-based stations 112.1-112.M. In an embodiment, one or moreground-based stations 112.1-112.M may be implemented as cell sites thatare configured to wirelessly communicate with other ground-basedstations, stations such as stations 103 and/or 105, and/or satellitessuch as one or more satellite communication systems 104.1-104.N inaccordance with any suitable number and/or type of communicationprotocols.

In other words, in various embodiments, one or more ground-basedstations 112.1-112.M may function to facilitate the delivery ofground-based services via ground-based network 110 to vehicle 102 aspart of an air-to-ground (ATG) network. In some embodiments, stations103 and/or 105 may communicate with one or more ground-based stations112.1-112.M to access the ground-based network. But in otherembodiments, stations 103 and/or 105 may access the ground-based networkvia communications with one or more satellite communication systems104.1-104.N, which in such a case function to facilitate communicationsbetween vehicle 102 and one or more ground-based stations 112.1-112.M.

One or more satellite communication systems 104.1-104.N may beconfigured to communicate with one or more stations (e.g., stations 103and/or 105) and one or more ground-based stations 112.1-112.M inaccordance with any suitable number and/or type of communicationsprotocols. To accomplish this, one or more satellite communicationsystems 104.1-104.N may be in a geosynchronous or non-geosynchronousorbit.

In various embodiments, vehicle 102 may include one or more computingsystems such as navigational systems, sensors, and/or other instrumentsthat facilitate navigational guidance and provide feedback regarding thevarious vehicle dynamics that may be updated during a flight or othertrip. These vehicle dynamics may include, for example, on-boardnavigational data to assist in piloting vehicle 102 to a particulardestination and may indicate the current location of vehicle 102 interms of latitude, longitude, altitude, and/or vehicle 102's currentspeed. Furthermore, the navigational data may include informationregarding the heading, roll, pitch, and yaw of vehicle 102. To provideadditional examples, the on-board navigational data may also include alatitude, longitude, and/or altitude of a particular target, such as oneor more satellite communication systems 104.1-104.N and/or or one ormore ground-based stations 112.1-112.M, for example, as furtherdiscussed below.

Vehicle 102 may also have one or more onboard computing systems thatstore data indicative of the geographic locations of one or moresatellite communication systems 104.1-104.N and/or one or moreground-based stations 112.1-112.M. Vehicle 102 may utilize thenavigational data to calculate a direction from stations 103 and/or 105towards a particular target based upon the vehicle's current locationand orientation in space as well as the known location of the target,such as one of satellite communication systems 104.1-104.N or one ofground-based stations 112.1-112.M, for example. Once this direction andorientation are known, a scan and skew angle may be calculated such thatan antenna beam pattern may be steered towards the desired target.

However, in doing so, the antenna gain may increase or decrease from theprevious scan and skew angle setting, thereby impacting the station'stransmitted EIRP with changes in antenna beam pattern. If the powerprovided to the station's antenna is held constant as the scan and skewangles of the antenna beam pattern are adjusted, the transmitted EIRPmay increase or decrease along with changes in the scan and skew angles.

Therefore, embodiments include stations 103 and/or 105 determining, foran updated scan and skew angle combination, an antenna gain and an EIRPspectral density (ESD) limit in accordance with the characteristics ofthe particular antenna used for signal transmission. Once these valuesare known, an antenna input power may be adjusted to compensate forthese changes to ensure that the transmitted EIRP is maintained at amaximum level dictated by the ESD limit at the new scan and skew angle.The details of these calculations are provided below with reference toFIG. 2.

FIG. 2 illustrates a block diagram of a station 200 in accordance withan embodiment of the present disclosure. In the present aspects, station200 may include a modem 202, an upconverter 204, a variable gainamplifier unit 206, a variable beamwidth antenna 212, and a processingunit 214. Station 200 may include additional, less, or alternatecomponents, including those discussed elsewhere herein. Furthermore, forthe sake of brevity, the embodiments herein are generally described inaccordance with station 200 performing transmission operations, and thusstation 200 is illustrated and described as part of a radio frequency(RF) transmit chain. However, it will be understood that the embodimentsdescribed herein may be reciprocated to be applicable to RF receivechains. In accordance with such embodiments, some components of station200 may be substituted for those implemented in accordance with an RFreceive chain. For example, upconverter 204 may be substituted for adownconverter (or a downconverter may be used in parallel withupconverter 204) to facilitate RF receive chain embodiments.

Again, station 200 may be associated with any suitable type of vehicle,such as an aircraft, for example, by being mounted, integrated, orotherwise located in a vehicle. In an embodiment, station 200 may be animplementation of station 103 or 105, for example, as shown in FIG. 1.Furthermore, station 200 may be configured to communicate with one ormore computing devices and/or sensors of the vehicle with which it isassociated. For example, if station 200 is associated with an aircraftand implemented as an ESAA, station 200 may be wired into the aircraft'selectrical system and/or be configured to transmit data to and/orreceive data from other parts of the aircraft's computing systems. In anembodiment in which station 200 is associated with an aircraft, station200 may be implemented, for example, as part of (or the entirety of) oneor more line replaceable units (LRUs) and/or any other suitablecombination of dedicated and/or shared aircraft components configured totransmit and/or receive data via variable beamwidth antenna 212, asdiscussed above with reference to FIG. 1.

In an embodiment, modem 202 may be configured to receive data signalsfrom one or more data sources within the vehicle in which station 200 isassociated and to modulate these data signals prior to upconversion byupconverter 204 and amplification by variable gain amplifier unit 206.These data signals may include, for example, part of data to betransmitted to one or more satellite communication systems and/orground-based stations during vehicle operation (e.g., during flight).Again, when receiving data, modem 202 may facilitate the demodulation ofdownconverted signals, which is not shown in FIG. 2 for purposes ofbrevity.

Variable gain amplifier unit 206 may be configured to amplify theupconverted data signals from upconverter 204 in accordance with avariable gain and to provide these signals as input to variablebeamwidth antenna 212 for transmission. Variable gain amplifier unit 206may include, for example, a gain trim block 208 and an amplifier block210. Variable gain amplifier unit 206 may be coupled to or otherwisecommunicate with processing unit 214, and processing unit 214 may setthe gain trim of gain trim block 208 to adjust the instantaneous poweroutput of variable gain amplifier unit 206. The instantaneous outputpower of variable gain amplifier unit 206, known herein as P_(out), isessentially the same as the input power to variable beamwidth antenna212, with the exception of any losses due to coupling between these twocomponents.

In various embodiments, variable beamwidth antenna 212 may beimplemented as any suitable type of antenna configured to transmitand/or receive data via a steerable beam pattern, which may be adjustedin accordance with any suitable type of beam steering techniques. In anembodiment, variable beamwidth antenna 212 may implement mechanicaland/or electrical beam steering control via processing unit 214. Forexample, variable beamwidth antenna 212 may receive one or more datasignals from processing unit 214 to cause mechanical and/or electricalchanges in variable beamwidth antenna 212, thereby causing variablebeamwidth antenna 212 to steer its transmitted beam pattern in aparticular direction associated with a particular scan and skew anglecombination. The embodiments described herein may be particularlyuseful, for example, when variable beamwidth antenna 212 is implementedas one or more antennas having a beamwidth with respect to a governingspectral mask that varies with location and/or orientation, such asphased array antennas, for example.

In various embodiments, processing unit 214 may be implemented as anysuitable number and/or type of processors configured to receive,monitor, and/or process data and to control and execute various tasksand/or functions of one or more components of station 200. For example,processing unit 214 may be configured to receive navigational data(e.g., NavData, as furtherer discussed below) from the various vehiclecomponents in which station 200 is associated. For example, the vehiclein which station 200 is implemented may utilize various communicationsystems, integrated navigational computers, storage components, LRUs,etc., which may be interconnected via one or more communication networksand constitute a portion of (or the entirety of) the vehicle'soperational system. In an embodiment, station 200 may communicate withand/or otherwise interact with one or more components of the vehicle'soperational system to facilitate one or more functions of theembodiments as described herein.

Again, this navigational data may include the current geographiccoordinates of the vehicle associated with station 200 (e.g., in termsof latitude and longitude), the orientation of the vehicle (e.g., yaw,pitch, and roll), as well as the location of a particular target towhich data should be sent and/or received (e.g., a satellitecommunication system or a ground-based station, as discussed above withrespect to FIG. 1). Using this information, processing unit 214 maycalculate a target scan and skew angle for variable beamwidth antenna212 in a desired direction based upon the navigational data to causevariable beamwidth antenna to steer its beam pattern in that direction,thus compensating for changes in the location and orientation of thevehicle in which station 200 is located.

In an embodiment, processing unit 214 may be configured to reference oneor more lookup tables (LUTs) that contain performance data related tovariable beamwidth antenna 212. This performance data is furtherdiscussed below and may include, for example, the ESD limit and theantenna gain for variable beamwidth antenna 212 for various scan andskew angle combinations and/or operating frequencies. Processing unit214 may access such LUTs via any suitable techniques, such ascommunications between processing unit 214 and one or more storagecomponents located in the vehicle associated with station 200, which arenot shown for purposes of brevity. To provide another example,processing unit 214 may include integrated storage to store these LUTslocally without having to communicate with other vehicle components. Thedata stored in these LUTs may be obtained, for example, by testing oneor more variable beamwidth antennas 212 having similar designcharacteristics, such that the LUTs contain data corresponding to knownor previously tested antenna performance parameters across an operatingrange of variable beamwidth antenna 212.

As discussed above, when steering the variable beamwidth antenna towardsdifferent targets, the different scan and skew angle combinations maycause the gain of variable beamwidth antenna 212 to vary, thus impactingthe transmitted EIRP. To compensate for these gain variations,embodiments include processing unit 214 leveraging the navigational datato dynamically adjust the output power of variable gain amplifier unit206. Furthermore, because the antenna gain and ESD limit are bothconsidered when calculating the new output power level for a new scanand skew angle combination, the transmitted EIRP of variable beamwidthantenna 212 is maximized towards a particular target to meet but notexceed the ESD limit. The details of this technique are furtherdiscussed below.

In an embodiment, processing unit 214 initially sets the amplifier to aninstantaneous maximum power P_(out), which corresponds to transmissionvia variable beamwidth antenna 212 at the ESD limit. The output power isa function of the ESD limit and antenna gain at a particular scan andskew angle, for a given location and aircraft attitude, which isrepresented below as Eqn. 1

$\begin{matrix}{{P_{out}\left( {\varphi,\psi} \right)} = {{{ESD}\left( {\varphi,\psi} \right)} + {10\; {\log_{10}\left( \frac{{ksym}/s}{4} \right)}} - {G_{ant}\left( {\varphi,\psi} \right)} + K}} & {{Eqn}\mspace{14mu} 1}\end{matrix}$

Where:

φ: scan angle in degrees;

ψ: skew angle in degrees;

P_(out) (φ, ψ): is the amplifier instantaneous maximum allowable outputpower in dBW as a function of φ and ψ;

ESD(φ, ψ): is the EIRP spectral density limit in dBW/4 kHz as a functionof φ and ψ;

ksym/s: is the modulated carrier rate in kilo-symbols per second;

G_(ant)(φ, ψ): is the variable antenna gain in dBi as a function of φand ψ; and

K: is cable loss in dB from variable gain amplifier unit 206 to variablebeamwidth antenna 212.

Eqn. 1, therefore, indicates the instantaneous maximum power amplifieroutput power needed to transmit at the ESD limit. In some cases of (φ,ψ), however, P_(out) (φ, ψ) will be limited by the rated output powerP_(rated), associated with variable gain amplifier unit 206.

In an embodiment in which station 200 is implemented in an aircraft andfacilitates satellite data transmission and reception, navigational data(NavData) may be processed by processing unit 214 and include, forexample, aircraft latitude (lat), aircraft longitude (long), satellitelongitude (slong), aircraft roll (roll), aircraft pitch (pitch), andaircraft yaw (yaw). As processing unit 214 receives updated NavDataduring flight (e.g., every second, every two seconds, every fiveseconds, etc.), a new target scan and target skew angle, which is usedto aim variable beamwidth antenna 212, φ⁺ and ψ⁺, respectively, may becalculated along with the instantaneous power output of variable gainamplifier unit 206 for these updated target scan and skew angles, whichis represented as P_(out) ⁺(φ⁺, ψ⁺). In other words, the target scan andskew angles φ⁺ and ψ⁺ may be represented as functions of these NavDataparameters, as shown below in Eqns. 2 and 3.

φ⁺=scan(lat,long,song,roll,pitch,yaw)  Eqn. 2:

ψ⁺=skew(lat,long,song,roll,pitch,yaw)  Eqn. 3:

Referring back to Eqn. 1, an antenna gain LUT associated with G_(ant)(φ, ψ) may be stored as an M×N table of various antenna gainscorresponding to various scan and skew angle combinations for variablebeamwidth antenna 212. Similarly, an ESD limit LUT associated withESD(φ, ψ) may be stored as an M×N table of various antenna gainscorresponding to various scan and skew angle combinations for variablebeamwidth antenna 212. In this way, once processing unit 214 calculatesthe target scan and skew angles φ⁺ and ψ⁺, the antenna gain LUT and theESD limit LUT may be referenced to calculate an instantaneous outputpower of variable gain amplifier P_(out) ⁺(φ⁺, ψ⁺) in accordance withEqn. 1, by substituting ESD(φ, ψ) with ESD(φ⁺, ψ⁺) and G_(ant)(φ, ψ)with G_(ant)(φ⁺, ψ⁺).

The antenna gain LUT and the ESD limit LUT may store data in accordancewith any suitable level of granularity. For example, antenna gain dataand ESD limit data may be stored for every five degrees of scan and skewangle combinations, every one degree, etc. In accordance with variousembodiments, processing unit 214 may determine whether the calculatedtarget scan and skew angles φ⁺ and ψ⁺ match entries stored in theantenna gain LUT and ESD limit LUT and, if a match is not found,processing unit 214 may perform bilinear interpolation to calculateESD(φ⁺, ψ⁺) and G_(ant)(φ⁺, 104 ⁺). This process is further describedbelow with reference to FIG. 3.

FIG. 3 illustrates a method flow 300 illustrating the amplifierinstantaneous output power calculations for new target scan and skewangles in accordance with an embodiment of the present disclosure.Method flow 300 may be performed by any suitable number and/or type ofprocessors. In an embodiment, method flow 300 may represent thecalculation steps performed by processing unit 214, for example, asshown and described with reference to FIG. 2.

Method 300 may start when one or more processors initiates an EIRPadjustment procedure to adjust amplifier output power to compensate fordifferences in ESD limits and antenna gain with changes in scan and skewangles (block 302). For example, method 300 may begin when a vehicle ispowered on or when a station is otherwise activated (block 302).

Method 300 may include one or more processors determining whetherupdated on-board navigational data (NavData) is received (block 304).This determination may be made, for example, via communications receivedfrom one or more vehicle components, as described above with referenceto FIG. 2. For example, processing unit 214 may receive updated on-boardNavData in accordance with a regularly recurring schedule (block 304).To provide another example, processing unit 214 may receive anindication represented by one or more data signals or other suitablecommunications that the on-board NavData has been updated (block 304).In any event, upon detecting that the on-board NavData has been updated,method 300 may proceed to calculate the target scan and skew angles φ⁺and ψ⁺ in accordance with Eqns. 2 and 3, as discussed above. Otherwise,method 300 may include maintaining the current amplifier power outputand continuing to monitor communications until new updated on-boardNavData is received (block 304).

Method 300 may include one or more processors calculating the targetscan and skew angles φ⁺ and ψ⁺ as a function of the NavData, asdiscussed above with respect to Eqns. 2 and 3 (block 306). This mayinclude, for example, using the NavData to calculate the target scan andskew angles φ⁺ and ψ⁺ based upon the orientation of the variablebeamwidth antenna in space and a required direction towards a particulartarget based upon that target's identified location (block 306).

Once the target scan and skew angles φ⁺ and ψ⁺ are calculated, method300 may include one or more processors determining whether these targetscan and skew angles φ⁺ and ψ⁺ match scan and skew angles stored in anantenna gain LUT and an ESD limit LUT (block 308). This determinationmay be made in accordance with any suitable techniques (block 308). Forexample, method 300 may include processing unit 214 determining whethertarget scan and skew angles φ⁺ and ψ⁺ match the scan and skew anglesstored in the antenna gain LUT and the ESD limit LUT within a thresholdtolerance (e.g., 1%, 5%, etc.), thus yielding a “match” when thiscondition is satisfied (block 308). To provide another example, method300 may include processing unit 214 determining whether target scan andskew angles φ⁺ and ψ⁺ match the scan and skew angles stored in each ofantenna gain LUT and ESD limit LUT by rounding and/or truncating thetarget scan and skew angles φ⁺ and ψ⁺. For example, after rounding ortruncating, the rounded or truncated target scan and skew angles φ⁺ andψ⁺ may then correspond directly to the scan and skew angles stored inantenna gain LUT and ESD limit LUT, thereby resulting in a match (block308).

Regardless of how this comparison is made and what constitutes a match,if a match for the target scan and skew angles φ⁺ and ψ⁺ is found in theantenna gain LUT and the ESD limit LUT (block 308), then method 300 mayproceed to use these values for the amplifier power output calculationsin accordance with Eqn. 1, for example (block 310).

Method 300 may include one or more processors calculating the targetamplifier instantaneous power output P_(out) ⁺(φ⁺, ψ⁺) in accordancewith Eqn. 1, for example, as discussed above (block 310). This mayinclude, for example, processing unit 214 calculating ESD(φ⁺, ψ⁺) andG_(ant)(φ⁺, ψ⁺) from their matching entries in the ESD limit LUT and theantenna gain LUT, respectively, for the LUT scan and skew angles thatcorrespond to the matching target scan and skew angles φ⁺ and ψ⁺ (block310).

However, if a match is not found for the target scan and skew angles φ⁺and ψ⁺ in either the ESD limit LUT or the antenna gain LUT (block 308),then method 300 may include processing unit 214 calculating ESD(φ⁺, ψ⁺)and/or G_(ant)(φ⁺, ψ⁺) in accordance with bilinear interpolation (block312). For example, the ESD limit LUT may be represented as atwo-dimensional M×N table, with M and N being associated with ranges ofscan and skew angles, respectively (or vice-versa). The cells in the ESDlimit LUT may also have ESD limit values for different intersectingcombinations of scan and skew angles. The antenna gain LUT may besimilarly represented, except that the antenna gain LUT may containdifferent antenna gain values for different intersecting combinations ofscan and skew angles.

Therefore, method 300 may include calculating G_(ant)(φ⁺, ψ⁺) usingbilinear interpolation in accordance with the two variables φ⁺ and ψ⁺.Specifically, the values for G_(ant)(φ⁺, ψ⁺) may be calculated from thetwo closest φ (left and right) in the antenna gain LUT, the two closestφ (top and bottom) in the antenna gain LUT, and their correspondingantenna gain values (block 312).

Similarly, method 300 may include calculating ESD(φ⁺, ψ⁺) using bilinearinterpolation in accordance with the two variables φ⁺ and ψ⁺.Specifically, the values for ESD(φ⁺, ψ⁺) may be calculated from the twoclosest φ (left and right) in the ESD limit LUT, the two closest φ (topand bottom) in the ESD limit LUT, and their corresponding antenna ESDlimit values (block 312).

Once G_(ant)(φ⁺, ψ⁺) and ESD(φ⁺, ψ⁺) are calculated, method 300 mayinclude one or more processors calculating the target amplifierinstantaneous power output P_(out) ⁺(φ⁺, ψ⁺) in accordance with Eqn. 1,as discussed above (block 314). This may include, for example,processing unit 214 utilizing the previously calculated ESD(φ⁺, ψ⁺) andG_(ant)(φ⁺, ψ⁺) via bilinear interpolation (block 312) in accordancewith Eqn. 1 (block 314).

Once P_(out) ⁺(φ⁺, ψ⁺) is calculated, method 300 may include one or moreprocessors calculating the output power of the variable gain amplifierthat is coupled to the variable beamwidth antenna as the lesser of thecalculated P_(out) ⁺ (block 310, 314) or the rated output power,P_(rated), associated with variable gain amplifier (block 316). Once theoutput power of the variable gain amplifier is set, method 300 mayinclude maintaining the current amplifier power output and continuing tomonitor communications until new updated NavData is received (block304). In this way, a maximum transmitted EIRP may be maintained over arange of scan and skew angles without exceeding the rated amplifierpower.

In an embodiments, once the amplifier output power is calculated, whichmay be done in accordance with method 300 discussed above, for example,processing unit 214 may measure the target amplifier power output. Forexample, variable gain amplifier unit 206 may have any suitable numberof attenuators or taps to facilitate this measurement. To provideanother example, processing unit 214 may obtain this data fromcommunications with various instruments, sensors, and/or computingdevices associated with the vehicle in which station 200 is located(e.g., the operational system of the vehicle, as discussed above). Oncethis power is determined, processing unit 214 may use this informationas feedback to calculate the transmitted EIRP, and to verify that thetransmitted EIRP is less than a maximum transmitted EIRP based upon theESD limit for the target scan angle and the target skew angle.

In other words, processing unit 214 may calculate a gain associated withgain trim block 208, which should result in the desired power outputlevel from variable gain amplifier unit 206. However, nonlinearities ofthe amplifier, errors introduced using bilinear interpolation,manufacturing tolerances among different tested variable beamwidthantennas, or other extraneous factors may result in the transmitted EIRPof variable beamwidth antenna 212 differing from the calculatedtransmitted EIRP in accordance with the calculated amplifier poweroutput. Therefore, by monitoring the actual amplifier power output,processing unit 214 may determine whether the transmitted EIRP hasexceeded the maximum allowable EIRP for a particular scan and skew anglecombination. If so, processing unit 214 may further reduce thecalculated output power via gain trim block 208 to ensure that themaximum EIRP limit is not exceeded.

FIG. 4A illustrates an example plot 400 showing changes in the effectiveisotropic radiated power (EIRP) limit, EIRP maximum, and EIRP minimumover a range of skew angles for a constant scan angle in accordance withan embodiment of the present disclosure. FIG. 4A illustrates performanceenhancement as a result of the embodiments described herein, in whichamplifier output power is adjusted as the variable beamwidth antenna issteered across varying skew angles ranging between 0 and 85 degreeswhile the scan angle is held constant at 35 degrees.

The curves in plot 400 represent the changes in EIRP as a function ofskew angle at a 35 degree scan angle, which may be represented asEIRP(35, φ). The EIRP curves shown in plot 400 are derived from Eqn. 4below.

$\begin{matrix}{{{EIRP}\left( {\varphi,\psi} \right)} = {{{ESD}\left( {\varphi,\psi} \right)} + {10\; {\log_{10}\left( \frac{{symbol}\mspace{14mu} {rate}}{4\mspace{14mu} {kHz}} \right)}}}} & {{Eqn}\mspace{14mu} 4}\end{matrix}$

Thus, the EIRP curves shown in plot 400 correspond to an EIRP calculatedin accordance with different ESD values. EIRP curve 402 is associatedwith the maximum EIRP limit in accordance with the maximum ESD limitvalue. EIRP curve 406, on the other hand, shows the result of utilizingthe minimum ESD limit to guarantee that the EIRP does not exceed theEIRP limit represented by EIRP curve 402 over the range of skew angles.As shown in FIG. 4A, as a result of the power output selection, EIRPcurve 406 is close to but does not exceed the maximum EIRP curve at thelower range of skew angles (e.g., less than 5 degrees). The use of theminimum ESD at the lower skew angle range therefore results in a lowerEIRP at higher skew angles.

The EIRP curve 404 represents the EIRP resulting from adjustingamplifier output power in accordance with Eqn. 1 and method 300, asdiscussed above. In other words, EIRP curve 404 indicates that becausethe amplifier power output is calculated using the maximum ESD limitvalue through the range of skew angles, that the transmitted EIRPsubstantially matches that of the EIRP limit curve 402. For example,with reference to FIG. 4A, at a point (35,20), the difference betweenEIRP curve 404 and EIRP curve 406 translates to approximately a 30%increase in EIRP, which is the result of evaluating

$10^{({- \frac{5.2}{10}})} = {30.2{\%.}}$

That is, because the EIRP curve 404 is changing across skew angles, thedifference between EIRP curve 404 and EIRP curve 406 also changes acrossskew angles. This increase in EIRP advantageously allows for faster datathroughput that would not otherwise be possible without the embodimentsdescribed herein.

FIG. 4A therefore illustrates that the adjustments to the variable gainof the variable gain amplifier unit 206 result in transmitting at anEIRP substantially equal to the maximum transmitted EIRP based upon theESD limit over the range of scan and skew angles (EIRP curve 404),without exceeding the maximum allowable transmitted EIRP (EIRP curve402).

FIG. 4B illustrates an example plot 450 showing changes in the amplifierinstantaneous output power over a range of skew angles for a constantscan angle, in accordance with an embodiment of the present disclosure.Similar to FIG. 4A, FIG. 4B shows data corresponding to a 35 degree scanangle for skew angles varying between 0 and 85 degrees. Amplifier poweroutput curve 452 corresponds to the adjusted amplifier output inaccordance with the embodiments described herein. For example, amplifierpower output curve 452 indicates that outPwr is the lesser of thecalculated P_(out) ⁺, or the rated output power P_(rated), for skewangles ranging between 0 and 85 degrees, as discussed above with respectto method 300. Amplifier power output curve 452, therefore, mayrepresent the amplifier power output corresponding to the EIRP curve404, as shown in FIG. 4A.

Amplifier power output curve 454, however, corresponds to the amplifieroutput associated with the lesser of the amplifier minimum output powercorresponding to the minimum ESD power or the rated output powerP_(rated) for skew angles ranging between 0 and 85 degrees. Amplifierpower output curve 454, therefore, may represent the amplifier poweroutput corresponding to the EIRP curve 406, as shown in FIG. 4A. FIG. 4Btherefore clearly illustrates the adjustments to amplifier power outputover a wide range of skew angles, resulting in the increased EIRP asdiscussed above with respect to FIG. 4A.

This detailed description is to be construed as exemplary only and doesnot describe every possible embodiment, as describing every possibleembodiment would be impractical, if not impossible. One may be implementnumerous alternate embodiments, using either current technology ortechnology developed after the filing date of this application.

Furthermore, although the present disclosure sets forth a detaileddescription of numerous different embodiments, it should be understoodthat the legal scope of the description is defined by the words of theclaims set forth at the end of this patent and equivalents. The detaileddescription is to be construed as exemplary only and does not describeevery possible embodiment since describing every possible embodimentwould be impractical. Numerous alternative embodiments may beimplemented, using either current technology or technology developedafter the filing date of this patent, which would still fall within thescope of the claims. Although the following text sets forth a detaileddescription of numerous different embodiments, it should be understoodthat the legal scope of the description is defined by the words of theclaims set forth at the end of this patent and equivalents. The detaileddescription is to be construed as exemplary only and does not describeevery possible embodiment since describing every possible embodimentwould be impractical. Numerous alternative embodiments may beimplemented, using either current technology or technology developedafter the filing date of this patent, which would still fall within thescope of the claims.

The following additional considerations apply to the foregoingdiscussion. Throughout this specification, plural instances mayimplement components, operations, or structures described as a singleinstance. Although individual operations of one or more methods areillustrated and described as separate operations, one or more of theindividual operations may be performed concurrently, and nothingrequires that the operations be performed in the order illustrated.Structures and functionality presented as separate components in exampleconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

Additionally, certain embodiments are described herein as includinglogic or a number of routines, subroutines, applications, orinstructions. These may constitute either software (e.g., code embodiedon a machine-readable medium or in a transmission signal) or hardware.In hardware, the routines, etc., are tangible units capable ofperforming certain operations and may be configured or arranged in acertain manner. In example embodiments, one or more computer systems(e.g., a standalone, client or server computer system) or one or morehardware modules of a computer system (e.g., a processor or a group ofprocessors) may be configured by software (e.g., an application orapplication portion) as a hardware module that operates to performcertain operations as described herein.

In various embodiments, a hardware module may be implementedmechanically or electronically. For example, a hardware module maycomprise dedicated circuitry or logic that is permanently configured(e.g., as a special-purpose processor, such as a field programmable gatearray (FPGA) or an application-specific integrated circuit (ASIC)) toperform certain operations. A hardware module may also compriseprogrammable logic or circuitry (e.g., as encompassed within ageneral-purpose processor or other programmable processor) that istemporarily configured by software to perform certain operations. Itwill be appreciated that the decision to implement a hardware modulemechanically, in dedicated and permanently configured circuitry, or intemporarily configured circuitry (e.g., configured by software) may bedriven by cost and time considerations.

Accordingly, the term “hardware module” should be understood toencompass a tangible entity, be that an entity that is physicallyconstructed, permanently configured (e.g., hardwired), or temporarilyconfigured (e.g., programmed) to operate in a certain manner or toperform certain operations described herein. Considering embodiments inwhich hardware modules are temporarily configured (e.g., programmed),each of the hardware modules need not be configured or instantiated atany one instance in time. For example, where the hardware modulescomprise a general-purpose processor configured using software, thegeneral-purpose processor may be configured as respective differenthardware modules at different times. Software may accordingly configurea processor, for example, to constitute a particular hardware module atone instance of time and to constitute a different hardware module at adifferent instance of time.

Hardware modules may provide information to, and receive informationfrom, other hardware modules. Accordingly, the described hardwaremodules may be regarded as being communicatively coupled. Where multipleof such hardware modules exist contemporaneously, communications may beachieved through signal transmission (e.g., over appropriate circuitsand buses) that connect the hardware modules. In embodiments in whichmultiple hardware modules are configured or instantiated at differenttimes, communications between such hardware modules may be achieved, forexample, through the storage and retrieval of information in memorystructures to which the multiple hardware modules have access. Forexample, one hardware module may perform an operation and store theoutput of that operation in a memory device to which it iscommunicatively coupled. A further hardware module may then, at a latertime, access the memory device to retrieve and process the storedoutput. Hardware modules may also initiate communications with input oroutput devices, and may operate on a resource (e.g., a collection ofinformation).

The various operations of example methods described herein may beperformed, at least partially, by one or more processors that aretemporarily configured (e.g., by software) or permanently configured toperform the relevant operations. Whether temporarily or permanentlyconfigured, such processors may constitute processor-implemented modulesthat operate to perform one or more operations or functions. The modulesreferred to herein may, in some example embodiments, compriseprocessor-implemented modules.

Similarly, the methods or routines described herein may be at leastpartially processor-implemented. For example, at least some of theoperations of a method may be performed by one or more processors orprocessor-implemented hardware modules. The performance of certain ofthe operations may be distributed among the one or more processors, notonly residing within a single machine, but deployed across a number ofmachines. In some example embodiments, the processor or processors maybe located in a single location (e.g., within a home environment, anoffice environment or as a server farm), while in other embodiments theprocessors may be distributed across a number of locations.

The performance of certain of the operations may be distributed amongthe one or more processors, not only residing within a single machine,but deployed across a number of machines. In some example embodiments,the one or more processors or processor-implemented modules may belocated in a single geographic location (e.g., within a homeenvironment, an office environment, or a server farm). In other exampleembodiments, the one or more processors or processor-implemented modulesmay be distributed across a number of geographic locations.

Unless specifically stated otherwise, discussions herein using wordssuch as “processing,” “computing,” “calculating,” “determining,”“presenting,” “displaying,” or the like may refer to actions orprocesses of a machine (e.g., a computer) that manipulates or transformsdata represented as physical (e.g., electronic, magnetic, or optical)quantities within one or more memories (e.g., volatile memory,non-volatile memory, or a combination thereof), registers, or othermachine components that receive, store, transmit, or displayinformation.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. For example, some embodimentsmay be described using the term “coupled” to indicate that two or moreelements are in direct physical or electrical contact. The term“coupled,” however, may also mean that two or more elements are not indirect contact with each other, but yet still co-operate or interactwith each other. The embodiments are not limited in this context.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the description. Thisdescription, and the claims that follow, should be read to include oneor at least one and the singular also includes the plural unless it isobvious that it is meant otherwise.

The patent claims at the end of this patent application are not intendedto be construed under 35 U.S.C. §112(f) unless traditionalmeans-plus-function language is expressly recited, such as “means for”or “step for” language being explicitly recited in the claim(s).

What is claimed is:
 1. An earth station aboard aircraft (ESAA),comprising: a variable beamwidth antenna configured to transmit inaccordance with a steerable beam pattern, the gain of the variablebeamwidth antenna changing for different scan and skew anglecombinations of the steerable beam pattern due to changes in the ESAA'slocation and attitude and antenna characteristics of the variablebeamwidth antenna; a processing unit configured to utilize on-boardnavigational data to calculate a target scan angle and a target skewangle for the steerable beam pattern to direct the steerable beampattern being towards a target station; and a variable gain amplifierunit coupled to the variable beamwidth antenna and to the processingunit, the variable gain amplifier configured to amplify input signals tothe variable beamwidth antenna in accordance with a variable gain toprovide a variable amplifier instantaneous power output, wherein theprocessing unit is further configured to (i) access an antenna gainlookup table (LUT) and an effective isotropic radiated power (EIRP)spectral density (ESD) limit LUT to calculate, in accordance with thetarget scan angle and the target skew angle, an antenna gain and an ESDlimit, respectively, (ii) calculate a target amplifier instantaneouspower output in accordance with the target scan angle and the targetskew angle based upon the calculated antenna gain and the calculated ESDlimit, and (iii) adjust the gain of the variable gain amplifier unitsuch that the amplifier power output is set to the target amplifierinstantaneous power output.
 2. The ESAA of claim 1, wherein the targetscan angle and the target skew angle result in the steerable beampattern being directed towards a target station to support ground-basedcommunications for an aircraft in which the ESAA is located, and whereinthe on-board navigational data includes one or more of: (i) a latitudeof the aircraft; (ii) a longitude of the aircraft; (iii) an altitude ofthe aircraft; (iv) a latitude of the target station; (v) a longitude ofthe target station; (vi) an altitude of the target station; (vii) a rollorientation of the aircraft; (viii) a pitch orientation of the aircraft;and (ix) a yaw orientation of the aircraft.
 3. The ESAA of claim 1,wherein the processing unit is further configured to update thecalculated antenna gain, the calculated ESD limit, and the calculatedtarget amplifier instantaneous power output as updated on-boardnavigational data is received, and to adjust the gain of the variablegain amplifier unit in accordance with the updated on-board navigationaldata.
 4. The ESAA of claim 3, wherein the processing unit is configuredto adjust the gain of the variable gain amplifier accordance with theupdated on-board navigational data over a range of scan and skew angles,and wherein the adjustments to the gain of the variable gain amplifierunit result in the variable beamwidth antenna transmitting at an EIRPsubstantially equal to but not exceeding a maximum transmitted EIRP overthe range of scan and skew angles in accordance with changes in the ESDlimit over the range of scan and skew angles.
 5. The ESAA of claim 1,wherein the processing unit is further configured to, when the targetscan and the target skew angle each match a respective scan and a skewangle included in each of the antenna gain LUT and the ESD limit LUTwithin a respective threshold value: (i) calculate the gain of thevariable beamwidth antenna as the antenna gain found in the antenna gainLUT for the scan and skew angles matching the target scan and the targetskew angle, respectively, and (ii) calculate the ESD limit of thevariable beamwidth antenna as the ESD limit found in the ESD limit LUTfor the scan and skew angles matching the target scan and the targetskew angle, respectively.
 6. The ESAA of claim 5, wherein the processingunit is further configured to, when the target scan and the target skewangle each do not match a respective scan and a skew angle included ineach of the antenna gain LUT and the ESD limit LUT within a respectivethreshold value: (i) calculate the gain of the variable beamwidthantenna by performing a bilinear interpolation of the antenna gainsassociated with the closest scan and skew angle found in the antennagain LUT, and (ii) calculate the ESD limit of the variable beamwidthantenna by performing a bilinear interpolation of the ESD limitsassociated with the closest scan and skew angle found in the ESD limitLUT.
 7. The ESAA of claim 1, wherein the processing unit is furtherconfigured to (i) measure the target amplifier instantaneous poweroutput, (ii) use the measured target instantaneous amplifier poweroutput to calculate the variable beamwidth antenna transmitted EIRP, and(iii) verify that the transmitted EIRP is less than a maximumtransmitted EIRP based upon the ESD limit for the target scan angle andthe target skew angle.
 8. An earth station aboard aircraft (ESAA),comprising: a variable beamwidth antenna configured to transmit inaccordance with a steerable beam pattern, the gain and effectiveisotropic radiated power (EIRP) spectral density (ESD) limit associatedwith the variable beamwidth antenna changing as a function of scan andskew angles of the steerable beam pattern; a processing unit configuredto calculate a target scan angle and a target skew angle for thesteerable beam pattern as updated on-board navigational data is receivedsuch that the target scan angle and the target skew angle result in thesteerable beam pattern being directed towards a target station tocompensate for changes in the location and orientation of the ESAA; anda variable gain amplifier unit coupled to the variable beamwidth antennaand to the processing unit, the variable gain amplifier configured toamplify input signals to the variable beamwidth antenna in accordancewith a variable gain to provide a variable amplifier instantaneous poweroutput, wherein the processing unit is further configured to (i)calculate, in accordance with the target scan angle and the target skewangle, an antenna gain and an ESD limit, (ii) calculate a targetamplifier instantaneous power output based upon the calculated antennagain and the calculated ESD limit corresponding to the calculated targetscan angle and the calculated target skew angle, and (iii) adjust thegain of the variable gain amplifier unit such that the amplifier poweroutput is set to the target amplifier instantaneous power output.
 9. TheESAA of claim 1, wherein the target station supports ground-basedcommunications for an aircraft in which the ESAA is located, and whereinthe on-board navigational data includes one or more of: (i) a latitudeof the aircraft; (ii) a longitude of the aircraft; (iii) an altitude ofthe aircraft; (iv) a latitude of the target station; (v) a longitude ofthe target station; (vi) an altitude of the target station; (vii) a rollorientation of the aircraft; (viii) a pitch orientation of the aircraft;and (ix) a yaw orientation of the aircraft.
 10. The ESAA of claim 8,wherein the processing unit is configured to adjust the gain of thevariable gain amplifier unit over a range of scan and skew angles asupdated on-board navigational data is received, and wherein theadjustments to the gain of the variable gain amplifier unit result inthe variable beamwidth antenna transmitting at an EIRP substantiallyequal to but not exceeding a maximum transmitted EIRP over the range ofscan and skew angles in accordance with changes in the ESD limit overthe range of scan and skew angles.
 11. The ESAA of claim 8, wherein theprocessing unit is further configured to calculate the gain of thevariable beamwidth antenna by referencing an antenna gain lookup table(LUT) that indicates changes in the gain of the variable beamwidthantenna over a range of scan and skew angles, and calculate the ESDlimit of the variable beamwidth antenna by referencing an ESD limit LUTthat indicates changes in the ESD limit of the variable beamwidthantenna over a range of scan and skew angles.
 12. The ESAA of claim 11,wherein the processing unit is further configured to, when the targetscan and the target skew angle each match a respective scan and a skewangle included in each of the antenna gain LUT and the ESD limit LUTwithin a respective threshold value: (i) calculate the gain of thevariable beamwidth antenna as the antenna gain found in the antenna gainLUT for the scan and skew angle combination matching the target scan andthe target skew angle, respectively, and (ii) calculate the ESD limit ofthe variable beamwidth antenna as the ESD limit found in the ESD limitLUT for the scan and skew angles matching the target scan and the targetskew angle, respectively.
 13. The ESAA of claim 11, wherein theprocessing unit is further configured to, when the target scan and thetarget skew angle each do not match a respective scan and a skew angleincluded in each of the antenna gain LUT and the ESD limit LUT within arespective threshold value: (i) calculate the gain of the variablebeamwidth antenna by performing a bilinear interpolation of the antennagains associated with the closest scan and skew angle found in theantenna gain LUT, and (ii) calculate the ESD limit of the variablebeamwidth antenna by performing a bilinear interpolation of the ESDlimits associated with the closest scan and skew angle found in the ESDlimit LUT.
 14. The ESAA of claim 1, wherein the processing unit isfurther configured to (i) measure the target amplifier instantaneouspower output, (ii) use the measured target instantaneous amplifier poweroutput to calculate the variable beamwidth antenna transmitted EIRP, and(iii) verify that the transmitted EIRP is less than a maximumtransmitted EIRP based upon the ESD limit for the target scan angle andthe target skew angle.
 15. A vehicle, comprising: an on-board systemconfigured to generate navigational data to track changes in thevehicle's location and attitude; and a station configured to: transmitsignals via a variable beamwidth antenna in accordance with a steerablebeam pattern, the gain and effective isotropic radiated power (EIRP)spectral density (ESD) limit associated with the variable beamwidthantenna changing as a function of scan and skew angles of the steerablebeam pattern; calculate a target scan angle and a target skew angle forthe steerable beam pattern as updated navigational data is received fromthe on-board system such that the target scan angle and the target skewangle result in the steerable beam pattern being directed towards atarget station to compensate for changes in the location and orientationof the vehicle; amplify input signals to the variable beamwidth antennain accordance with a variable gain to provide a variable amplifierinstantaneous power output; calculate, in accordance with the targetscan angle and the target skew angle, an antenna gain and an ESD limit,calculate a target amplifier instantaneous power output based upon thecalculated antenna gain and the calculated ESD limit corresponding tothe calculated target scan angle and the calculated target skew angle;and adjust the gain of the variable gain amplifier unit such that theamplifier power output is set to the target amplifier instantaneouspower output.
 16. The vehicle of claim 15, wherein the navigational dataincludes: (i) a latitude of the vehicle; (ii) a longitude of thevehicle; (iii) an altitude of the vehicle; (iv) a latitude of the targetstation; (v) a longitude of the target station; (vi) an altitude of thetarget station; (vii) a roll orientation of the vehicle; (viii) a pitchorientation of the vehicle; and (ix) a yaw orientation of the vehicle.17. The vehicle of claim 15, wherein the station is further configuredto adjust the gain of the variable gain amplifier unit over a range ofscan and skew angles as updated navigational data is received from theon-board system, and wherein the adjustments to the gain of the variablegain amplifier unit result in the variable beamwidth antennatransmitting at an EIRP substantially equal to but not exceeding amaximum transmitted EIRP over the range of scan and skew angles inaccordance with changes in the ESD limit over the range of scan and skewangles.
 18. The vehicle of claim 15, wherein the station is furtherconfigured to (i) calculate the gain of the variable beamwidth antennaby referencing an antenna gain lookup table (LUT) that indicates changesin the gain of the variable beamwidth antenna over a range of scan andskew angles, and (ii) calculate the ESD limit of the variable beamwidthantenna by referencing an ESD limit LUT that indicates changes in theESD limit of the variable beamwidth antenna over a range of scan andskew angles.
 19. The vehicle of claim 18, wherein the station is furtherconfigured to: when the target scan and the target skew angle each matcha respective scan and a skew angle included in each of the antenna gainLUT and the ESD limit LUT within a respective threshold value: (i)calculate the gain of the variable beamwidth antenna as the antenna gainfound in the antenna gain LUT for the scan and skew angles matching thetarget scan and the target skew angle, respectively, and (ii) calculatethe ESD limit of the variable beamwidth antenna as the ESD limit foundin the ESD limit LUT for the scan and skew angles matching the targetscan and the target skew angle, respectively, and when the target scanand the target skew angle each do not match a respective scan and a skewangle included in each of the antenna gain LUT and the ESD limit LUTwithin a respective threshold value: (i) calculate the gain of thevariable beamwidth antenna by performing a bilinear interpolation of theantenna gains associated with the closest scan and skew angle found inthe antenna gain LUT, and (ii) calculate the ESD limit of the variablebeamwidth antenna by performing a bilinear interpolation of the ESDlimits associated with the closest scan and skew angle found in the ESDlimit LUT.
 20. The vehicle of claim 15, wherein the station is furtherconfigured to (i) measure the target amplifier instantaneous poweroutput, (ii) use the measured target instantaneous amplifier poweroutput to calculate the variable beamwidth antenna transmitted EIRP, and(iii) verify that the transmitted EIRP is less than a maximumtransmitted EIRP based upon the ESD limit for the target scan angle andthe target skew angle.